Current sources are commonly used for several applications to provide voltage or current signals to one or more different loads. Often, such loads require voltages or currents, which are different from a voltage or current supplied by an externally arranged supply source. Such supply sources may include batteries, for example. It is therefore a common practice to power a current source with a power source to convert the voltage provided by the externally arranged supply source to the required voltage for the load. For instance, mobile applications, including transmitters, receivers and the like, may require voltages and current signals different from the voltage and current signal provided by a battery. Accordingly, current sources with DC/DC converters or charge pump are used to provide the respective signals to the load. Further, current sources are often used for driving light emitting diodes.
In addition, different loads may require different voltages or currents for its respective operation. Still, the current sources providing the respective signals to the load connected thereto are in turn coupled to a common charge pump or DC/DC converter. The current sources now comprise an adjustment device which receives a supply voltage and provides respective voltage and current signals to the load. The adjustment device often comprises an adjustable resistive element for the purpose of providing current to a load connected thereto. The voltage applied to the current source is therefore divided between the load and the adjustment device of the respective current source itself. The loss of power across the current source may now increase with higher voltage drops across the adjustment device, which therefore reduces the overall efficiency.
On the other hand, power sources, like for instance a charge pump may be operated on different discrete output voltage levels. A multiplication factor can be assigned to each output voltage, wherein the output voltage is given by the multiplication factor times the supply signal applied to the power source.
FIG. 13 shows the architecture of a prior art digital power source. A charge pump may provide an output voltage Vgen to a current source connected thereto in response to a respective multiplication factor, said factor derived by a signal provided by the current source.
If the factor is equal or lower than “1”, the charge pump generates an output voltage Vgen lower than the supply voltage VBAT. Accordingly, the charge pump may generate higher output voltages Vgen than the supply voltage VBAT if the multiplication factor is greater than 1. Typical charge pumps can operate on some different multiplication factors. In dependence on the load connected to the current source, it may become necessary to increase or decrease the multiplication factor in the set of available values of the multiplication factor to provide sufficient current and voltage to the load.